Frequently there arises a need to weld a small part to a larger part at an acute angle. Unless hard tooling is available, it is difficult to support the smaller part in the desired position until the joint is tack-welded. The usual manner of doing this is to clamp the smaller part to a piece of angle iron or such in order to hold the part in position. Often, no suitable configuration of supporting structure is available in the shop.
There are numerous types of clamps commercially available for clamping parts in position for welding. For example, there is a holding device available consisting of two magnets connected by a link. The magnets can swivel on parallel axes at each end of the link to allow the base of the magnets to be oriented at an acute or obtuse angle to each other in one plane. Neither the clamps nor the magnet assembly allows for accurate positioning and positive holding of a small part which must be supported at an angle between two planes.
The patent literature discloses a variety of adjustable joints used in positioning fixtures.
U.S. Pat. No. 4,196,518 issued to Benzaria disclosed a double ball-and-socket joint used to support dental bridge molds wherein both joints are simultaneously locked and unlocked with a single lever.
U.S. Pat. No. 4,515,333 issued to Pugh disclosed an adjustable support for instruments used in microsurgery. The ball of a ball joint is nested within clamping rings which are forced by springs against the surface of the ball to lock the ball in a desired position. The clamps are forced apart by air pressure to release the ball. An extension on one side of the ball supports an instrument while an opposite extension supports a counter balancing weight. The presence of the counterweight would interfere with the freedom of positioning that is required in applications intended for the present invention.
U.S. Pat. No. 4,767,231 issued to Wallis disclosed a method of providing an adjustable joint between two intermediate sections which utilizes dual ball-and-socket joints provided with a means for manually locking the joint. U.S. Pat. No. 4,557,623 issued to Tella disclosed a robotic wrist joint which utilizes two hemispherical elements located in opposite ends of a cylindrical enclosure. The mounting stems of the hemispherical elements are attached to a robot arm and to a work holder respectively. The joint is free to articulate in the nominal condition. Supplying air pressure to one port on the cylindrical body causes the joint to align the stems of the hemispherical elements to a common centerline. Supplying air pressure to a second port on the body causes the joint to rigidly lock.
U.S. Pat. No. 4,702,465 issued to McConnell disclosed a ball joint suitable for positioning an Extremity Support mounted on a hospital operating table. The joint is slidably mounted on a support bar providing that the joint can be positioned at arbitrary locations along the length of the table. The joint is normally held in the locked condition by a spring and unlocked by pressing on a foot pedal.
U.S. Pat. No. 4,834,519 issued to Twisselmann, disclosed a ball joint suitable for positioning surgery microscopes. The joint is nominally held in the locked condition by a spring and manually released by pressing on a lever.